1. Field of the Invention
The present invention relates to a High Electron Mobility Bipolar Transistor (BiHEMT), and more specifically to a sub-collector/separating layer (i.e. the separating layer is an epi layer that vertically separates the heterojunction bipolar transistor and pseudomorphic high electron mobility transistor) with carbon concentration within 5×1017 cm−3 and 1×1020 cm−3, and/or the oxygen concentration within 5×1018 cm−3 and 1×1020 cm−3.
2. The Prior Arts
Compared with the Si based FET, heterojunction bipolar transistors (HBTs) with better capability of power handling and linearity are more suitable for the application of power devices, especially for the power amplifiers in the smart phones and tablet PCs. The pseudomorphic high electron mobility transistors (pHEMTs) that is the device with very high mobility are undoubtedly suitable for the high speed switches and low noise amplifiers (LNA). To take the advantages from both, the original concept of manufacturing the BiHEMT is based on silicon-based BiCMOS by integrating the HBT and pHEMT on a single epi stack. The integration HBT and pHEMT can reduce the size of the module from original two chips to one chip, the package cost, and increase the functionality.
However, one problem in the manufacturing of the BiHEMT in the prior arts is that the defects in the sub-collector and separating layer are diffusive during the epitaxial growth process, and thus cause the elements and dopants in the neighboring layers for example, the InGaP etch stop layer in the pHEMT, the AlGaAs Schottky layer and the Si doped AlGaAs donor layers) diffuse outward. This leads to channel mobility degradation and on-resistance increase in the pHEMT. Additionally, it makes process sensitive to the growth parameters such as growth temperature and difficult to control. Therefore, it is desired a new structure for the BiHEMT to solve the above issues.